Being skeletally immature is a normal developmental stage indicating a person’s bones are still growing, particularly in length. It is not a disorder or abnormality but a sign of childhood and adolescence. Understanding this status helps gauge a child’s physical development and remaining growth potential.
The Science of Growth Plates
Skeletal immaturity is defined by open growth plates, known as epiphyseal plates. These plates are areas of specialized cartilage located near the ends of long bones. You can think of them as factories where new cartilage is produced and then replaced by bone tissue. This process, called endochondral ossification, is what allows bones to lengthen and pushes the ends of the bone away from its shaft.
Prominent growth plates are found in the long bones of the legs and arms, with significant ones located at the knee, wrist, and shoulder.
How Skeletal Age Is Determined
Doctors determine skeletal maturity by assessing “bone age,” which can differ from a child’s chronological age. This difference might indicate a growth problem or be a normal variation. The most common method is an X-ray of the left hand and wrist, as its many small bones develop in a predictable sequence.
A radiologist compares the child’s X-ray to a standardized reference, like the Greulich and Pyle atlas, which contains images of average skeletal appearance at different ages. The development of the bones and the thinness of the growth plates help the doctor assign a skeletal age. For specific evaluations like scoliosis, the Risser sign, which observes bone formation on the pelvis, may also be used.
Injury Risks and Activity Considerations
The growth plates are the weakest part of a developing skeleton, making skeletally immature individuals more susceptible to certain injuries. Forces that might cause a ligament sprain in an adult can instead lead to a growth plate fracture in a child. These fractures are classified using systems like the Salter-Harris classification to help guide treatment.
Repetitive stress from sports can also lead to overuse injuries affecting the growth plates, a condition known as apophysitis. Examples include Osgood-Schlatter disease at the knee or Little League elbow. Periods of rapid growth are a time of particular risk because muscles and tendons can become tight as bones lengthen, increasing tension across the plates. For this reason, focusing on proper athletic technique and avoiding overtraining are important for injury prevention.
A sudden, sharp pain during an activity could signal a fracture, while a persistent ache might indicate an overuse issue. If a growth plate injury is suspected, a physical exam and X-rays are used for diagnosis.
Reaching Skeletal Maturity
Reaching skeletal maturity involves the gradual thinning and hardening of the growth plates. Influenced by hormones during puberty, the cartilage cells in the plates stop dividing as rapidly. Eventually, the cartilage is completely replaced by solid bone in a process called growth plate closure, at which point longitudinal bone growth is no longer possible.
For girls, this process typically completes between ages 14 and 16, while for boys, it generally occurs between 16 and 19, though individual timing can vary. A person is considered “skeletally mature” when these growth plates have fully closed and their bones have reached their final adult length.